1. Field of the Invention
The present invention relates to an image scanning method used in a scanner. More specifically, the present invention discloses an image scanning method for increasing a resolution of a document image used in a scanner.
2. Description of the Prior Art
A scanner is a widespread peripheral device for scanning documents and producing corresponding image data. The scanner has some additional functions, such as faxing image data to a fax machine over telephone lines, transmitting the image data in e-mail format over a network, or connecting to a printer to print the image data.
Please refer to FIG. 1 and FIG. 2. FIG. 1 is a diagram of a scanner 10 according to the prior art. FIG. 2 is a functional block diagram of the scanner 10. The scanner 10 comprises a housing 12, control circuitry 22 for controlling operations of the scanner 10, a scanning module 18 installed inside the housing 12, and a step motor 20 installed inside the housing 12 and electrically connected between the control circuitry 22 and the scanning module 18. As shown in FIG. 1, a transparent platform 14 is set on the housing 12 for a document 16 to be placed on. While the scanning module 18 scans the document 16, the control circuitry 22 controls the step motor 20 to drive the scanning module 18 step by step so as to scan the document 16.
Please refer to FIG. 3, which is a diagram of a movement of the scanning module 18 when utilizing a prior art image scanning method. As shown in FIG. 3, when the document 16 is placed on the transparent platform 14 for performing a scanning pass, the scanning module 18 moves forward continuously along an X direction from a starting end 17 in a fixed space corresponding to one step of the step motor 20, and performs actions of exposure and images reading until the scanning module 18 reaches a stopping end 19 of the scanner 10. Then, the scanning module 18 moves backward to the starting end 17 from the stopping end 19 so as to complete a scanning procedure.
To double the resolution of the scanned image, the prior art scanner utilizes the control circuitry 22 to control the step motor 20 to move a step unit which is half the original step distance of the step motor 20 so as to scan the document 16. In this way, pixel numbers of the scanned image of the document 16 are doubled. When the scanning module 18 completes the scanning procedure to scan the document 16, the resolution of the document 16 image increases twofold.
Nevertheless, from a standpoint of motor control, when the scanner 10 doubles the resolution of the scanned image, the step motor 20 uses half-step control. Under half-step control, a scanning rate of the step motor 20 is slower, in contrast with full-step control, so that it is easy to cause missteps of the scanning module 18, which leads the scanning procedure to produce errors if the scanner 10 uses the half-step control too much. Furthermore, in the backward process, after completing the scanning procedure, the scanning module 18 only does oblique auto-correcting, auto-reducing and bright contrast correction image processing, without taking image samples from the document 16. In today""s image processing field, a data-transmitting mode of the scanner 10 is increasingly fast, and a rate of image processing accelerates. Under these conditions, very little time is spent performing image processing during the backward process. It seems a waste of the rest of that time not to take image samples from the document 16.
It is therefore a primary objective of this invention to provide an image scanning method for increasing resolution of a document image used in a scanner.
The present invention, briefly summarized, discloses an image scanning method used in a scanner. The scanner includes a housing, a transparent platform set on the housing for a document to be placed on, a scanning module installed inside the housing for scanning the document, and a step motor for driving the scanning module step by step so as to scan the document. After completing a first scanning pass, the scanning module moves a predetermined distance, which corresponds to non-integer steps of the step motor, so that when the scanning module performs a second scanning pass, sampling positions of the second scanning pass are different from sampling positions of the first scanning pass.
It is an advantage of the present invention that the image scanning method still utilizes full-step control of the step motor to perform a scanning procedure. The full-step control of the step motor allows the step motor to maintain a normal step rate so that time of the scanning procedure is reduced, and further avoids problems of motor missteps for increasing resolution of the document when performing the scanning procedure.
These and other objectives and advantages of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.